What's stated above is all correct. In English, a key signature corresponds to a key which is stated as a note (A, B, C, D, E, F, G) and then Major and Minor for the scale you are using. The note used corresponds to the first note of the scale.
For the rules of thumb for figuring out the Major scales from the key signature, see the wikipedia entry for "Key Signatures" and look in the section "Table of key signatures" for the rules of thumb about figuring out the key in major . I've summarized it below.
No sharps or flats is C major
One flat is F major
For more than one flat, the (major) key is the next-to-last (second from right) flat.
For any number of sharps, take the last sharp displayed in the key signature and go up one semitone to get the (major) key. For example, in the A major key signature, the last sharp is G♯, so go up one semitone from G♯ to get A major.
The same key signature also applies to a minor scale. The corresponding minor scales would be a third below the major scale, ie C Major has the same key signature as A minor.
In many cases, when a musician looks at a key signature, an English speaker will only say the key and not "major" or "minor" afterwards. So, most musicians will look at a key signature with one sharp and say that the music is "in G" without adding the word "major". In other words, if a speaker says that a piece is in "G", that means "G major" but if a piece uses a minor scale, then you must say "minor" after the key note, ie, "E minor."
Typically, the key signatures using sharps are most often used for major scales, but flats are the typical used for minor scales. Therefore (getting to the original question), two flats is most likely in G minor (but it could also be in "Bb major").